A difficult problem of microsystems is inducing and controlling forces. In particular, it is desired to reduce friction forces between two elements of a microsystem moving with respect to each other.
In general, there are several methods to actuate elements of micrometer dimensions on micrometer scales:
An electrostatic force can be asserted. However, the movable element would need to provide a mechanical/electrical contact to a voltage source. Moreover, the electrostatic force is an attractive one in most cases. It is difficult to induce a repulsive actuation force based on electrostatic actuation.
A magnetic force can be asserted: Again, the movable element would need to provide either a mechanical/electrical contact or comprise a magnetic particle. The requirement for a coil and a magnetic particle adds complexity to the system. Additionally, it is rather difficult to set up magnetic field conditions such that movements on a micrometer scale can be controlled.
The movable element could also be mechanically coupled to a mechanical actuator such as a piezo actuator. Of course, the movable element would need to provide a mechanical contact.
“Knudsen forces on microcantilvers”, A. Passian et al., Journal of Applied Physics, Volume 92, Number 10, pages 6326-6333, 15 Nov. 2002, and “Thermal Transpiration at the Microscale: A Crookes Cantilever”, A. Passian et al., Physical Review Letters, Volume 90, Number 12, 28 Mar. 2003, both show the occurrence of Knudsen forces in a microsystem between two surfaces at different temperatures which one surface belongs to a microcantilever and the other surface belongs to a sample substrate. The microcantilever is attached to the sample substrate. Both documents are referred to in the following as “Passian et al.”.
For an application where a movable element shall be actuated and cannot have a mechanical contact or a magnetic particle attached and at least a repulsive force shall be generated, no solution is known.